The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in the background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Mobile telecommunication systems, such as those based on the 3GPP defined UMTS and Long Term Evolution (LTE) architecture, are able to support more sophisticated services than simple voice and messaging services offered by previous generations of mobile telecommunication systems. For example, with the improved radio interface and enhanced data rates provided by LTE systems, a user is able to enjoy high data rate applications such as video streaming and video conferencing on mobile communications devices that would previously only have been available via a fixed line data connection.
The demand to deploy fourth generation networks is therefore strong and the coverage area of these networks, i.e. geographic locations where access to the networks is possible, is expected to increase rapidly.
However, although the coverage and capacity of fourth generation networks is expected to significantly exceed those of previous generations of communications networks, there are still limitations on network capacity and the geographical areas that can be served by such networks. These limitations may, for example, be particularly relevant in situations in which networks are experiencing high load and high-data rate communications between communications devices, or when communications between communications devices are required but the communications devices may not be within the coverage area of a network.
In order to address these limitations, in LTE release-12 the ability for LTE communications devices to perform device-to-device (D2D) communications is introduced. D2D communications allow communications devices that are in close proximity to directly communicate with each other, both when within and when outside of a coverage area or when the network fails. The ability for communications devices to operate both inside and outside of coverage areas makes LTE systems that incorporate D2D capabilities well suited to applications such as public safety communications, for example. Public safety communications require a high degree of robustness whereby devices can continue to communicate with one another in congested networks and when outside a coverage area.
Whilst D2D communications techniques can provide an arrangement for communicating between devices when the communications devices are outside a coverage area provided by mobile communications network, the D2D communications techniques can also provide an arrangement for extending a coverage area of the mobile communications network, when one of the communications devices is within the coverage area and another is outside the coverage area. There may also be situations in which D2D communications between communications devices which are both within a coverage area of a mobile communications network are supported (thus allowing network capacity to be increased, for example).
There are several issues to consider when implementing such D2D communication techniques, however. For example, in a coverage extension scenario, in which a first communications device which is out of the coverage area of a mobile communications network performs communication with the mobile communications network via a second communications device which is within the coverage area of the mobile communications network (the second communications device therefore acting as a D2D relay node), the system must manage selection of a relay node when the first communications device initially leaves the coverage area of the mobile telecommunications network, switching of relay nodes when the first communications device leaves the coverage area of one relay node and enters the coverage area of another, and determination of the suitability of various second communication devices for acting as the relay node. Similarly, even if both the first and second communication devices are within the coverage area of the mobile telecommunications network, the system needs to manage which of the second communication devices is selected as the relay node and to manage mobility of the first communications device as it moves from the coverage area of one second communications device or base station to another second communications device.
The need to perform such management of LTE D2D communications in a wireless telecommunications network results in additional data processing in the network. It is therefore desirable to consider alternative arrangements to LTE D2D communication which allow coverage extension, increased network capacity and/or increased network efficiency.